There are several answers to this question – depending on what you mean by “solar energy”.
If you mean solar power produced by solar panels that directly convert sunlight energy into electrical energy, then the answer is “high.”
But if you mean solar power stored in a battery that can be used at a later time, the answer is “low.”
High-Quality Solar Energy
High-quality solar energy is defined as solar energy that has been carefully collected, converted into electrical energy, and stored in a manner that minimizes losses. This type of solar energy can be thought of as the “best” or “cleanest” form of solar power. When you compare it to other less-quality solar energies, you get a clearer idea of what quality means in this context. (This is a very broad concept, but it makes for an easy introduction to this topic.)
The main reason why high-quality solar energy is so valuable is that it has a much higher peak power than other forms of solar energy. A high-peak-power-rated solar cell or module can handle a much higher current than a low-peak-power-rated one, so it can convert more sunlight energy into electrical energy. (A high-peak-power solar cell or module also tends to be more expensive than its low-peak-power counterpart.)
For an in-depth analysis of the difference between high- and low-quality solar energy, check out our post on the topic – [Does Solar Energy Have High or Low Net Energy? An In-Depth Analysis]. You will learn more in there than you have from this entire article, but it’s also a pretty long read. (If you’re short on time, just go to the gist for the summary.)
Low-Quality Solar Energy
To make a long story short, low-quality solar energy is anything but high-quality solar energy that has not been appropriately treated before being converted into electrical energy. (You can think of it as solar energy that has been poorly stored or handled.)
This type of solar energy usually has a much lower peak power than high-quality solar energy, so it can’t handle as much current. The current rating of a solar cell or module determines how much electrical load it can handle – the higher the current rating, the higher the power the solar cell or module can produce. (Some low-quality solar energies also have a significantly reduced efficiency compared to high-quality solar energies.)
Because of its low peak power, a low-quality solar energy source can only produce a lower amount of electrical energy compared to high-quality solar energy. In order to compensate for this lower yield, you need to either use more solar cells or modules, or keep reloading the battery more frequently. (Recycle batteries as much as possible, since they are a finite resource and can be damaged by exposure to water or electricity.)
Peak Power
Peak power is a measurement of the maximum amount of electrical power a certain rated solar cell or module can produce during some specific time period. This measurement can be determined by directly measuring the output of the solar cell or module under a defined amount of sunlight (usually calibrated on a sunny day), or it can be measured statistically by using a solar simulator to generate artificial sunlight inside a lab. (A solar simulator emits light that is similar to sunlight; it’s often used in laboratories to accurately measure how much power a solar cell or module can produce under different conditions.)
The “peak” in peak power refers to the fact that this measurement is taken during a time period when the power produced by the solar cell or module is at its highest – typically around noon in summer and winter, and directly after sunrise and before sunset in spring and autumn.
A high-quality solar cell or module has a high peak power because it can handle more current than a low-quality solar cell or module. A high-quality solar cell or module can also be more efficient at converting sunlight energy into electrical energy than a low-quality solar cell or module. Furthermore, the efficiency of a high-quality solar product decreases more slowly with increasing current than the efficiency of a low-quality solar product, which means it can handle a higher current with a lower loss of efficiency. (In other words, a high-quality solar cell or module is more “current-proof” than its low-quality counterpart.)
Efficiency
Efficiency is the ratio of the amount of electrical energy produced by a solar cell or module to the amount of sunlight energy fed into it. A highly efficient solar cell or module can convert a large portion of the light it receives into electrical energy without suffering from a significant loss of efficiency. (This means it can produce more electrical energy for a given amount of sunlight than a less-efficient solar product.)
Because they are more efficient at converting light into electricity, high-quality solar cells and modules have a higher efficiency rating than low-quality solar cells and modules. But the efficiency of a high-quality solar cell or module decreases more quickly with increasing current, so it can handle a higher current with a lower efficiency than its low-quality counterpart. (This makes a high-quality solar cell or module less suitable for use in direct sunlight where a higher current is required.)
Yield
The yield of a solar cell or module refers to the total amount of electricity generated by the solar cell or module over a given period of time. (In most cases, the period of time over which the yield of a solar cell or module is determined is a full day or night, depending on the type of installation.)
A highly-efficient solar cell or module has a higher yield than a less-efficient solar cell or module, because it can generate more electricity for a given amount of sunlight. The efficiency of a solar cell or module decreases with increasing current, so a higher-yield version of a solar cell or module can handle a higher current with a lower efficiency than its lower-yield counterpart.
Durability
The durability of a solar cell or module refers to the physical integrity of the device – the ability of the device to function without serious defects for a given amount of time. This measurement can be determined by directly measuring the lifetime of the solar cell or module under a given amount of sunlight, or by statistically analyzing the operating time of the device in different conditions. (The higher the number, the more durable the device.)
A highly-durable solar cell or module can function for a given amount of time in different conditions (for example, high temperatures or high altitudes) without significant decrease in output or efficiency. (This kind of solar cell or module is more reliable than those with a lower durability rating, which means it will likely function longer before failing.)
Because they have a longer lifespan, high-quality solar cells and modules are more durable than low-quality ones. But high-quality solar cells and modules are more expensive than their low-quality counterparts, so it’s often better to go for the less-expensive option if durability is not a concern.
Net Energy
Finally, we come to the most important point in this article: What is net energy?
If you compare the total amount of energy produced by a solar cell or module — which is defined as the sum of its power and efficiency — to the total amount of energy used to generate and supply it, you will get a number that indicates the overall efficiency of the system: the higher the number, the more efficient the system. (If you’re not familiar, Joule’s Law states that the product of a given electric load and voltage is directly proportional to the product of the kinetic energy and speed of the electrons in the load.)
This measure of efficiency — called net energy — of a solar cell or module is more significant than you might think. For one thing, the energy-efficiency rating of a solar cell or module is directly proportional to the retail price of the product – so it’s in the industry’s best interest to keep it as high as possible. (They actually have to work harder to convince customers to buy their product thanks to its low efficiency – not to mention the fact that they have to work harder to generate electricity with a lower efficiency rating.)